A fuel cell system is a system configured to generate electric power and heat by an electrochemical reaction between a fuel gas (hydrogen-containing gas) and an oxidizing gas (for example, air) supplied to a fuel cell. The electric power generated by a common domestic fuel cell system is supplied to some of home-use electric power loads (for example, electrical appliances, such as lights and air conditioners). The heat generated by the electric power generation is recovered by cooling water supplied into the fuel cell. The recovered heat is recovered as hot water through, for example, a heat exchanger and supplied to domestic heat loads (for example, heat utilizing devices, such as water heaters and floor heating).
Since an infrastructure for supplying the hydrogen-containing gas necessary in the electric power generating operation of the fuel cell system is not developed, the fuel cell system is normally provided with a reformer configured to generate the hydrogen-containing gas. The reformer generates the hydrogen-containing gas by causing a steam-reforming reaction in a reforming catalyst between a material gas (for example, city gas (natural gas)) and water.
In such fuel cell system, a method for utilizing the water recovered in the system, that is, a method for supplying the water by itself is adopted in many cases as a supply source of the water supplied to the reformer and the cooling water. One example of a method for recovering the water in the fuel cell system is a method for recovering the water by cooling and condensing steam contained in the fuel gas and oxidizing gas discharged from the fuel cell.
However, the water (hereinafter referred to as “recovered water”) recovered in the fuel cell system does not contain sterilizing components, such as chloride components. In addition, when recovering the recovered water, the recovered water flows through various parts and pipes in the fuel cell system. Therefore, the recovered water contains a small amount of impurities, such as organic constituents (TOC; Total Organic Carbon). Thus, the recovered water is in a state preferable for the proliferation of microorganisms, such as fungi and bacteria.
Therefore, the microorganisms, such as the fungi, may proliferate in the system by the infiltration of the microorganisms, such as the fungi, through an exhaust port through which the oxidizing gas is discharged after the recovery of the water, a discharge port through which a surplus of the recovered water is discharged, or the like. Then, by the proliferation of the microorganisms, the clogging or narrowing of a passage through which the recovered water flows may occur, and this may deteriorate a water supply function and a water purification function.
To solve the above problems, a fuel cell cogeneration system (see PTL 1, for example) is known, in which the temperature of the water is temporarily increased to a predetermined temperature (For example, 70° C.), necessary for heat sterilization, or higher. In addition, a fuel cell power generation system (see PTL 2, for example) is known, which includes: a recovered water tank configured to store recovered water recovered from an exhaust gas of the fuel cell; a first purifying unit configured to purify the recovered water; and a second purifying unit having a heatproof temperature higher than the heatproof temperature of the first purifying unit, and in which when the temperature of the recovered water in the recovered water tank is higher than the heatproof temperature of the first purifying unit, the water is prevented from flowing through the first purifying unit.    PTL 1: Japanese Laid-Open Patent Application Publication No. 2002-270194    PTL 2: Japanese Laid-Open Patent Application Publication No. 2007-234477